Generally, when mounting a power-supply circuit element such as a power module (a power module will be described below as a representative example of power-supply circuit elements) on the printed circuit board in a printed circuit board unit, terminal pins of the power module are bonded to printed wire (copper foil) of a main circuit on the printed circuit board. An inverter module is used as a power module in, e.g., a refrigeration apparatus (the refrigeration apparatus described herein includes an air conditioning apparatus), and such a power module is connected between an external power supply and an inverter compressor (target to be driven). In such a configuration, current supplied through terminal pins of the power module flows through copper foil of a main circuit of a printed circuit board, and then is supplied to the compressor which is the target to be driven.
Recently, even the size of a high-current power module has been reduced with improvement in performance of semiconductor devices. Thus, a space between terminal pins provided on the power module tends to be reduced. There is a power module which is directly soldered to a printed circuit board, and which is rated at high current of 50-100 A. A small-size power module has a smaller cross-sectional area of a terminal pin, resulting in an increase in temperature of the terminal pin due to heat from a chip of the power module. Then, the temperature in a connecting section of a printed circuit board and the terminal pin increases, and exceeds a heat resistant temperature of the printed circuit board. Thus, the printed circuit board cannot be used up to rated current.
If the printed circuit board unit is rated at the above-described high current level in the circuit board unit used for, e.g., the inverter control of the air conditioner, it is necessary to expand a cross-sectional area of the printed wire (copper foil), which contains the connecting section in order to lower a resistance value. However, in order to lower the resistance value, it is necessary to expand the width of the copper foil because the thickness of the copper foil cannot be extremely increased.
The expansion of the copper foil width is contradictory to the reduction in space between the terminal pins of the power module. Thus, it is not practical that, in the printed circuit board unit using the high-current power module having the narrower space between the terminal pins, the width of the copper foil is expanded in order to apply high current.
Patent Document 1 discloses a configuration in which a terminal base to be bonded to a printed circuit board is used as a connecting member of an electrical circuit, and a terminal pin of a power module are screwed to such a terminal base.